Most aerodynamic surfaces, such as airplane leadings edges, are thin metallic structures that lack rigidity. The parts lack rigidity due to the thickness of the sheet material leading to low rigidity in bending and torsion, particularly for long parts such as engine inlet lip skins and wing leading edges. The lack of rigidity makes the parts very difficult to inspect to the dimensional requirements. Leading edges on the next generation of aircraft are being manufactured to tighter tolerances as a method to reduce drag and fuel burn. To ensure these tighter tolerances are met, advances are required in the methods to verify the tolerances of both the part and assembly.
One type of an airplane leading edge is an engine inlet lip skin. A typical lip skin is illustrated in FIGS. 1-4. Multi-piece lip skins 20 and single piece lip skins 20a are known in the art. The lip skin 20, 20a is formed into a thin, aerodynamically shaped metal skin which is generally circular when viewed in plan view as shown in FIGS. 2 and 3. The lip skin 20, 20a is usually formed of aluminum, but may be formed of other impact resistant materials, such as titanium. The lip skin 20, 20a includes a curved leading nose 22 having an internal face 24 and an external face 26, an outer trailing surface 28 having an internal face 30 and an external face 32, the outer trailing surface 28 extending from the nose 22 and terminating in an edge 34, and an inner trailing surface 36 having an internal face 38 and an external face 40, the inner trailing surface 36 extending from the nose 22 and terminating in an edge 42. As a result of the structure, a pocket 44 is formed by the nose 22, the outer trailing surface 28 and the inner trailing surface 36. The lip skin 20, 20a is formed to be smooth and devoid of irregularities and discontinuities to reduce drag and to avoid the creation of turbulence. The nose 22 provides a smooth transition between the outer and inner trailing surfaces 28, 36, while creating a small frontal area to reduce drag. The outer trailing surface 28 is longer than the inner trailing surface 36. The multi-piece lip skin 20 is formed of a plurality of sectors 46 which are affixed together by known means to form the completed lip skin 20. The multi-piece lip skin 20 is flexible and if the lip skin 20 were placed on a flat surface, the lip skin 20 would not hold its shape due to the thinness of the metal. The single-piece lip skin 20a is more rigid than the multi-piece lip skin 20, however, it also cannot be placed on a flat surface and hold its shape due to the thinness of the metal.
Lip skins have complex shapes that are often out-of round and difficult to manufacture. Lip skins are typically produced by multiple-stage deep draw operations, bulge forming, or spin forming, requiring complex and costly tooling and time consuming multi-step processing. As a result, it can be difficult to meet the tolerance requirements.
A method is provided herein which allows a part, such as a lip skin, to constrain the lip skin at the locations the lip skin would be constrained upon assembly on the airplane and inspected to dimensional requirements by a measurement system. Other features and advantages will become apparent upon a reading of the attached specification, in combination with a study of the drawings.